\section{Conclusion}

In this work we have presented a checkpoint restart framework that 
successfully integrates Xen VM checkpoints with NILFS disk snapshots. 
Based on an resource aware placement mechanism offered by SigLM, this 
framework can be utilized to migrate VMs off failed nodes to other 
suitable host machines. Since disk snapshots are also maintained, the 
work done by the VM prior to failure is preserved and the rollback 
overhead is minimized. Our prototypical implementation encompasses a 
host level cluster manager subsystem that controls all managerial 
functions of the hosts in the cluster. These functions include keeping 
track of VMs, periodically checkpointing all VMs and also detecting 
invoking SigLM and migrate function in failure situations. An XML-RPC 
framework was used to handle functon calls between the cluster manager 
and node server instances running on all hosts in the cluster. 

Experiments show that our system is capable of periodically saving 
checkpoints of all the VMs in the cluster without any signicant 
downtime of the unaware VM. In addiditon to this, we were also able to 
accurately detect failures in the system and successfully leverage 
SigLM as a placement engine. Using the results from SigLM, we were 
successfully able to migrate VMs to a new host keeping rollback 
overheads to a minimum. Although this operation is proving to be a 
costly one, we hope to address this bottleneck in our future work.

Additionally we have also laid the groundwork to integrate an energy 
aware decision framework which would be applied to the output of 
SigLM. This would allow us to explicitly consider energy when 
making placement decisions.
